1. Field of the Invention
The present invention relates to a control system, for a series-type hybrid vehicle, that makes an electric motor drive a vehicle by use of an internal combustion engine for generating electric power.
2. Description of the Related Art
In general, in a series-type hybrid vehicle, there is mounted an electric motor as a driving force source for a vehicle. This electric motor is supplied with electric power from a battery, and the battery is charged with the output of an electric power generator. Then, this electric power generator is driven by a relatively small internal combustion engine (engine).
This kind of vehicle is controlled by an electronic control system. Speaking in detail, in a vehicle, there are provided a hybrid control unit that controls an electric power generator and an electric motor and an engine control unit that controls an engine; these control units manage and control each other based on a signal for detecting an operation status of the vehicle. For example, in the case where the engine is driven, the hybrid control unit calculates a requested engine output based on a battery status or the like and outputs it to the engine control section. Then, the engine control unit controls a fuel injection amount for satisfying the requested engine output (e.g., refer to Japanese Patent Application Laid-Open No. 2006-132391).
In a hybrid vehicle control system disclosed in Japanese Patent Application Laid-Open No. 2006-13239, a plurality of electronic control units that controls two or more respective constituent elements of a vehicle are configured to be capable of transmitting information to one another by way of a communication line, and by use of transmitted information from the other control units, each of the plurality of electronic control units performs collaborative control. Specifically, there is provided a hybrid control unit that calculates an engine output value for making an electric motor and an engine operate in a collaborative manner, while controlling the electric motor; the hybrid control unit transmits an engine output command value to the engine control unit that controls the engine, by way of the communication line. In response to the engine output command value, the engine control unit calculates control amounts such as a throttle opening degree, a fuel injection amount, and an ignition timing, and optimally controls the engine, based on the control amounts.
However, in the hybrid vehicle control system disclosed in Japanese Patent Application Laid-Open No. 2006-13239, in the case where there occurs an abnormality in the communication system between the engine control unit and the hybrid control unit, the engine control unit cannot receive information such as a requested engine rotation speed from the hybrid control unit; therefore, power generation torque that can maintain the operation of the system cannot be detected. As a result, because there occurs a difference between an actual power consumption and a generated electric power, there may be caused a case where the battery is excessively charged or excessively discharges electricity.
Accordingly, there has been proposed a technology that provides measures for raising the safety in travel by a vehicle and reducing the risk of causing damage to the electric system, in the case where there occurs an abnormality in the communication system between the engine control unit and the hybrid control unit (e.g., refer to Japanese Patent Application Laid-Open No. 2004-208368 and Japanese Patent Application Laid-Open No. 2002-285905).
In Japanese Patent Application Laid-Open No. 2004-208368, when an abnormality occurs in the communication system, the hybrid control unit makes the motor output torque to be zero and implements magnetic-field weakening control when the engine (motor) rotation speed is higher than a set speed; when the engine rotation speed is lower than the set speed, the engine control unit controls the engine in such a way that the engine rotation speed does not exceed the upper limit; when the engine rotation speed is higher than the set speed, the engine control unit controls the engine in such a way that there is produced target engine torque with which the engine rotation speed becomes lower than the upper limit; after the engine rotation speed has become lower than the upper limit, the engine control unit controls the engine in such a way that the engine rotation speed does not exceed the upper limit.
In Japanese Patent Application Laid-Open No. 2002-285905, when an abnormality occurs in the communication system, the engine control unit selects the present operation status and the target state of a vehicle from a plurality of operation statuses of the vehicle preliminarily set based on a plurality of control parameters, and stepwise selects, based on a predetermined priority, an appropriate transition path from a plurality of transition paths through which the operation state of the vehicle is moved from the present operation status to the target state; then, the engine control unit controls the engine in accordance with the selected transition path.
However, the technologies disclosed in Japanese Patent Application Laid-Open No. 2004-208368 and Japanese Patent Application Laid-Open No. 2002-285905 are the ones that are applied to a parallel-type hybrid vehicle that utilizes both an internal combustion engine and an electric motor, as a driving power source for the vehicle; therefore, application of the foregoing technologies to a series-type hybrid vehicle poses the following problems.
In the case where the technology disclosed in Japanese Patent Application Laid-Open No. 2004-208368 is utilized and an abnormality occurs in the communication between the engine control unit and the hybrid control unit while the engine is driven, when the engine control unit does not have any means for detecting a wheel rotation speed or when the engine control unit cannot detect the wheel rotation speed due to a communication abnormality, the engine control unit cannot detect power generation torque that can maintain the operation of the system; therefore, there exists only a method in which power generation is continued while the engine is driven in such a way that the engine rotation speed does not exceed the upper limit or a method in which the engine is stopped so that power generation is stopped. In addition, once the engine is stopped, the engine and the electric motor do not rotate together in a series-type hybrid vehicle; therefore, the engine cannot be restarted.
As discussed above, when the engine control unit cannot detect the battery remaining amount or the vehicle power consumption, there is caused a difference between the actual power consumption and the electric power generated by the electric power generator; therefore, the battery may excessively be charged or may excessively discharge electricity. As a result, it becomes difficult to move the vehicle to an intended place, for example, to make the vehicle travel to a repair shop; moreover, there may be caused damage to the electric system for driving the electric motor in the vehicle, for example, the motor controlling unit may suffer damage due to an excessive voltage.
Additionally, in the case where the technology disclosed in Japanese Patent Application Laid-Open No. 2002-285905 is utilized, because based on a plurality of control parameters, the statuses of the engine and the electric motor are estimated in detail, the operation state of the vehicle can more appropriately move to the fail-safe mode; however, in fact, there has been a problem that in order to detect a plurality of control parameters, it is required to add sensor inputs or an estimation means and the logic and the software become complicated. Moreover, because there are two or more control parameters, it takes a long time to deal with them.